This invention relates to a method of extracting curcumin from turmeric root and, in particular, to a method which yields various water soluble and oil soluble forms of curcumin.
Ground turmeric root (Curcuma Longa) has a spicy flavor and is commonly used as a condiment and coloring agent in currys, rice and other foods. The root also provides a source of curcumin which is the coloring matter in the root. Curcumin which has been extracted by traditional methods is an orange-yellow crystalline powder. It has been used in various ways to color consumable products such as ice cream, cheese, pickles, vegetable oil shortening, oleo margarine, medicines and others.
The traditional commercial method of extracting curcumin starts with grinding the hard precooked and dried turmeric roots, called fingers, until a powder is formed which has a granule size about equal to ordinary sugar. The ground root is then put in a vessel through which hexane is circulated to remove some of the oils from the root. This step is followed by further washings with a mixture of hexane and alcohol in which curcumin is soluble. Upon further treatment with more concentrated alcohol, the colorful curcumin is extracted and is dissolved in alcohol. Treatment is continued until the root no longer gives up curcumin to the alcohol. At the end of the process, the alcohol-curcumin mixture is gummy and is called resin. The residual root solids are then filtered out and the alcohol and other volatiles which may be present are distilled off, leaving the usable crystalline powdered curcumin. Inspection of the residual or spent root before discharging it to waste reveals that it has retained a substantial amount of its basic coloring matter, namely, the curcumin.
The chemical composition of curcumin is given in the Merck Index where several references to publications dealing with its extraction are also given. Curcumin is described as an orange-yellow crystalline powder, melting point 180.degree. C., yielding a brownish-red color with alkali and a light-yellow color with acids, soluble in alcohol and glacial acetic acid and insoluble in ether and water.
The traditional commercial process outlined above for producing curcumin has several undesirable aspects. One results from the use of methanol as the extraction alcohol. It is used because it has a good affinity for curcumin, thus increasing yield, but it is toxic and should not be present in a food product. Alcohols and hexane are also combustible which is obviously undesirable.
Another undesirable aspect is that the end product, crystalline curcumin, is not soluble in water. It is also not directly soluble in fatty based substances. To make it soluble and usable as a dispersed coloring agent, it must first be dissolved in a substance which will make it soluble or dispersible in a water based or fatty based food product. Most commonly, it is dossolved in a material which is well known as PS-80 which is a variety of polysorbate. PS-80 is costly and its use requires another step and more handling in a food coloring operation, thus increasing complexity and cost of production. Moreover, when the curcumin coloring matter is dissolved in polysorbate, a water based product, such as the fluid in commercially preserved pickles, does not exhibit the degree of clarity nor the light-yellowish tinge that is desired in products of this kind.
Prior curcumin extraction methods also failed to remove all of the curcumin from the ground turmeric root within a reasonable process time. The natural root as received usually contains 3% to 4.5% of curcumin. As much as 25% of the original curcumin in the root is believed to remain in the ground root waste in some instances when the traditional extraction process is used. This is inferred from the relatively intense orange-yellow color which the residual spent root has. Obviously, to be able to extract substantially all of the curcumin from the root would be desirable from an economic point of view since the curcumin is the valuable part of the root.